This file doesn't contain actual text, but an image (probably scanned). Therefore you can't select individual words or sentences in it.
Your only option is to run Text Recognition on it (under Tools - Text Recognition). If the results are successful then you'll be able to select the text as with other files.
I started to recognize it as an image. However, I have one question: Why is the file extension .pdf not .jpg or other image file extensions by default?
Anyway, I tried your method. A message is displayed: 'Acrobat could not perform recognition (OCR) on this page because: This page contains renderable text'. I ignored the message and clicked on OK, and I finally got the PDF and can select text now.
But the issue is that the PDF is now greater than 3 mb (the original was 345 kb). It contains only four pages; another journal article downloaded from the same database contains more than 4 pages, and it is only 1245kb.
Is this normal?
- It's a PDF because that's the format the person who created it decided to use. There are many benefits to using a PDF over an image file, even for scanned pages, such as: You can have multiple pages in the same file, you can add comments to the file, you can perform OCR on it (like you did), etc.
- The file size can increase because the OCR process adds additional data to the file, especially it embeds the fonts that are used in it. If there are multiple fonts then the file size can increase dramatically.
One thing you can try, though, is to use the Save As command and save the file under a new name. This will force an optimization and might help reduce the file-size somewhat.
I used Save As command but to no avail: The file is still the same size. Nevertheless, this is not a major concern.
Thank you for your assistance.